• Korean Journal of Materials Research
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• v.20 no.4
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• pp.204-209
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• 2010

Recent high efficiency electronic devices have been found to have heat emission problems. As for LEDs, an excessive increase in the device temperature causes a drop of the luminous efficiency and circuit lifetime. Therefore, heat release in the limited space of such electronic parts is very important. This is a study of the possibility of using a coating of carbon materials as a solution for the thermal emission problem of electronic devices. Powdered carbon materials, cokes, carbon blacks, amorphous graphite, and natural flakes were coated with an organic binder on an aluminum sheet and the subsequent thermal emissivity was measured with an FT-IR spectrometer and was found to be in the range of $5{\sim}20\;{\mu}m$ at $50^{\circ}C$. The emissivity of the carbon materials coated on the aluminum sheet was shown to be over 0.8 and varied according to carbon type. The maximum thermal emissivity on the carbon black coated-aluminum surface was shown to be 0.877. The emissivity of the anodized aluminum sheets that were used as heat releasing materials of the electronic parts was reported to be in the range of 0.7~0.8. Therefore, the use of a coating of carbon material can be a potential solution that facillitates heat dissipation for electronic parts.

• Journal of the Korean institute of surface engineering
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• v.42 no.3
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• pp.109-115
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• 2009

Magnesium is one of the lightest metals, and magnesium alloys have excellent physical and mechanical properties such as high stiffness/weight ratios, good castability, good vibration and shock absorption. However their poor corrosion resistance, wear resistance, hardness and so on, have limited their application. To improve these defects, many techniques are developed. Micro arc oxidation(MAO) is a one of the surface treatments under anodic oxidation in which ceramic coating is directly formed on the surface of magnesium alloy. In this study, the characteristics of anodic film were examined after coating the AZ31B magnesium alloy through the MAO process. MAO was carried out in potassium hydroxide, potassium fluoride, and various concentration of sodium silicate in electrolyte. The morphology and chemical composition of the coating layer were characterized by SEM, XRD, EPMA and EDS. The hardness of anodic films was measured by micro-vickers hardness tester. As a result, the morphology and composition of anodic film were changed by concentration of sodium silicate. Thickness and Si composition of anodic film was increased with increasing concentration of sodium silicate in electrolyte. The hardness of anodic film was highly increased when the concentration of sodium silicate was above 40 g/l in electrolyte.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.8
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• pp.875-881
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• 2004

Fundamental results obtained from an atomic force microscope (AFM) chemically-induced direct nano-lithography process are presented, which is regarded as a simple method for fabrication nm-scale devices such as superconducting flux flow transistors (SFFTs) and single electron tunneling transistors (SETs). Si cantilevers with Pt coating and with 30 nm thick TiO coating were used as conducting AFM tips in this study. We observed the surfaces of superconducting strip lines modified by AFM anodization' process. First, superconducting strip lines with scan size 2 ${\mu}{\textrm}{m}$${\times}$2 ${\mu}{\textrm}{m}$ have been anodized by AFM technology. The surface roughness was increased with the number of AFM scanning, The roughness variation was higher in case of the AFM tip with a positive voltage than with a negative voltage in respect of the strip surface. Second, we have patterned nm-scale oxide lines on ${YBa}-2{Cu}_3{O}_{7-x}$ superconducting microstrip surfaces by AFM conductive cantilever with a negative bias voltage. The ${YBa}-2{Cu}_3{O}_{7-x}$ oxide lines could be patterned by anodization technique. This research showed that the critical characteristics of superconducting thin films were be controlled by AFM anodization process technique. The AFM technique was expected to be used as a promising anodization technique for fabrication of an SFFT with nano-channel.

• Korean Journal of Materials Research
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• v.25 no.2
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• pp.107-112
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• 2015

The oxide films formed on etched aluminum foils play an important role as dielectric layers in aluminum electrolytic capacitors. $Y_2O_3$-doped $ZrO_2$ (YZ) films were coated on the etched aluminum foils by sol-gel dip coating, and the electrical properties of YZ-coated Al foils were characterized. YZ films annealed at $450^{\circ}C$ were crystallized into a cubic phase, and as the $Y_2O_3$ doping content increased, the unit cell of $ZrO_2$ expanded and the grain size decreased. The etch pits of Al foils were filled by YZ sol when it dried at atmospheric pressure after repeating for several times, but this step could essentially be avoided when being dried in a vacuum. YZ-coated foils indicated that the specific capacitance and dissipation factor were $2-2.5{\mu}F/cm^2$ and 2-4 at 1 kHz, respectively, and the leakage current and withstanding voltage of films approximately 200 nm thick were $5{\times}10^{-4}A$ at 21 V and 22 V, respectively. After being anodized at 500 V, the foils exhibited a specific capacitance and dissipation factor of $0.6-0.7{\mu}F/cm^2$ and 0.1-0.2, respectively, at 1 kHz, while the leakage current and withstanding voltage were $2{\times}10^{-4}-3{\times}10^{-5}A$ at 400 V and 420-450 V, respectively. This suggests that YZ film is a promising dielectric that can be used in high voltage Al electrolytic capacitors.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.158-158
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• 2017

Titanium and its alloys have been used in the field dental and orthopedic implants because of their excellent mechanical properties and biocompatibility. Despite these attractive properties, their passive films were somewhat bioinert in nature so that sufficient adhesion of bone cells to implant surface was delayed after surgical treatment. Recently, plasma electrolyte oxidation (PEO) of titanium metal has attracted a great deal of attention is a comparatively convenient and effective technique and good adhesion to substrates and it enhances wear and corrosion resistances and produces thick, hard, and strong oxide coatings. Silicon(Si), Zinc(Zn), and Manganese(Mn) have a beneficial effect on bone. Si in particular has been found to be essential for normal bone and cartilage growth and development. And, Zn has been shown to be responsible for variations in body weight, bone length and bone biomechanical properties. Also, Mn influences regulation of bone remodeling because its low content in body is connected with the rise of the concentration of calcium, phosphates and phosphatase out of cells. The objective of this work was research on bone-like apatite morphology on Si-Zn-Mn-hydroxyapatite coating on Ti-6Al-4V alloy by plasma electrolytic oxidation. Anodized alloys were prepared at 280V voltage in the solution containing Si, Zn, and Mn ions. The surface characteristics of PEO treated Ti-6Al-4V alloy were investigated using XRD, FE-SEM, and EDS.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.152-152
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• 2017

Titanium and its alloys have been widely used for biomedical applications. However, the use of the Ti-6Al-4V alloy in biomaterial is then a subject of controversy because aluminum ions and vanadium oxide have potential detrimental influence on the human body due to vanadium and aluminum. Hence, recent works showed that the synthesis of new Ti-based alloys for implant application involves more biocompatible metallic alloying element,such as, Nb, Hf, Zr and Mo. In particular, Nb and Hf are one of the most effective Ti ${\beta}$-stabilizer and reducing the elastic modulus. Plasma electrolyte oxidation (PEO) is known as excellent method in the biocompatibility of biomaterial due to quickly coating time and controlled coating condition. The anodized oxide layer and diameter modulation of Ti alloys can be obtained function of improvement of cell adhesion. Silicon (Si) and magnesium (Mg) has a beneficial effect on bone. Si in particular has been found to be essential for normal bone and cartilage growth and development. In vitro studies have shown that Mg plays very important roles in essential for normal growth and metabolism of skeletal tissue in vertebrates and can be detected as minor constituents in teeth and bone. Therefore, in this study, Si and Mg coatings on the hydroxyapatite film formed Ti-29Nb-xHf alloys by plasma electrolyte oxidation has been investigated using several experimental techniques. Ti-29Nb-xHf (x= 0, 3, 7 and 15wt%, mass fraction) alloys were prepared Ti-29Nb-xHf alloys of containing Hf up from 0 wt% to 15 wt% were melted by using a vacuum furnace. Ti-29Nb-xHf alloys were homogenized for 2 hr at $1050^{\circ}C$. The electrolyte was Si and Mg ions containing calcium acetate monohydrate + calcium glycerophosphate at room temperature. The microstructure, phase and composition of Si and Mg coated oxide surface of Ti-29Nb-xHf alloys were examined by FE-SEM, EDS, and XRD.

• Applied Chemistry for Engineering
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• v.8 no.5
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• pp.784-789
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• 1997

Aluminium solid electrolytic capacitor in which electroconducting polypyrrole(PPy) is used as an electrolyte is studied. Pyrrole(Py) is electrochemically synthesized using the etched and anodized aluminium foil electrode($Al_2O_3$) as an anode on which the thin layer of chemicalpolymerized PPy as a pre-coating layer is formed previously by chemical oxidative polymerization(CP). Investigating the effects of the polymerization conditions on the electrical characteristics of resulting capacitors, the capacitors which were obtained from the galvanostatic electrolysis of pyrrole containing sodium p-toluenesulfonate(TsONa) under the currents of $2.0{\sim}4.0mA/unit(6.5{\times}10mm)$, showed the most superior properties.

• Molecular & Cellular Toxicology
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• v.4 no.3
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• pp.192-198
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• 2008

A variety of titanium (Ti) and its alloys are used in the clinical procedures of bone regeneration for periodontal and dental implant therapies. This study was performed to determine the effect of different surface dental implant materials on biologic responses of a MG-63 human osteoblast-like cell line. MG-63 cells were cultured on Ti coated with hydroxyapatite (HA), calcium metaphosphate (CMP), anodized (A), which compared with non-coated Ti (control). The appearances of surface of dental implant materials and the morphology of these cells were assessed by scanning electron microscopy (SEM). The gene expression profiles of MG-63 cells cultured on Ti were examined by human cDNA microarray (1,152 elements). The expression of several genes was up- and down-regulated by different surfaces of dental implant materials. Interesting, the genes correlated with cellular adhesion and extra cellular matrix (ECM) formation were enhanced, in accordance surface morphology of the dental implant materials used.

• Journal of Korean society of Dental Hygiene
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• v.7 no.4
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• pp.471-479
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• 2007

The purpose of this study was to examine the optimum condition of impulse during the anodic spark oxidation applying pulse current as well as to find the excellent condition for HA precipitation the after electrochemical hydrothermal treatment by cathode reduction method. After anodic spark oxidation, the anodized specimen and the Pt plate connected cathode and anode, respectively. Hydrothermal treatment performed at 90, 120, $150^{\circ}C$ for 2 hours in the electrolyte containing $K_2HPO_4$, $CaCl_2{\cdot}2H_2O$, Tris(Hydroxymethyl)-$(CH_2OH)_3\;CNH_2$(Aminomethane), and NaCl. The optimum impulse voltage for anodic spark oxidation was 350V. The optimum pulse cycle measured at 10 mS. The HA crystals precipitated excellently by cathode reduction at $150^{\circ}C$ for 2 hours. The phases of anatase, rutile, and HA coating on the surface of modified titanium surface immersed in Hanks' solution for 3weeks were detected by XRD measurement and the intensity of HA crystal phase has increased by temperature and time of hydrothermal treatment. According to the our experiments, we found that Pure Ti will be good materials of bioactivity and biocompatibility.

• Korean Journal of Materials Research
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• v.29 no.11
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• pp.657-663
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• 2019

In this work, we study physical and mechanical properties of oxide films formed on AZ91D magnesium alloy by plasma anodization at different temperatures. It is found that the higher the electrolyte temperature, the lower is the breakdown voltage of oxide layer. This is probably because films formed at higher temperatures are thinner and denser. Moreover, electrolyte temperature plays an important role in the physical properties of the films. As the electrolyte temperature increases from 20 to $50^{\circ}C$, the hardness of the oxide layer increases. Friction test against steel balls indicates that wear scars become narrower for films formed at higher temperatures because the films are harder, as indicated by the Vickers hardness. The thinner and denser nature of the oxide film formed at $50^{\circ}C$ is also advantageous for heat transfer when film is used as a heat sink. Laser flash test results show very fast heat transfer for AZ91D with plasma anodized oxide layer formed at higher temperatures.